The later standards are NOT better for all applications. Any designation SJ or subsequent is an "Energy Saving" oil. These are designed for late model engines running very high oil pressure in very tight tolerances.The Japanese equivalent of our SAE is JASO. They designated a standard -MA- that is roughly equivalent to our older SG. This allows a much higher percentage of heavy metals and other additives that provide a cushioning effect on on gears and other areas with large clearances, high loads, and low oil pressures. Does this sound anything like an Enfield engine? Also, the very properties that make the SJ oils flow also will cause leakage issues in older designed or older manufactured engines. I really recommend a motorcycle specific oil that meets the MA or SG specification. Not only is it better for the Enfield, it will also enhance the transmission in unit construction engines. You cannot get these oils at Auto Zone. "Safe" for motorcycles is not the same. I know it's more expensive, but your local cycle store should carry the right oil. I use Torco (in my truck too!),but any of the name brands such as Spectro, Bel-Ray, Hondaline, etc. will be fine.